iPhone 3G Will Not Slide to Unlock/Power Off?

I just got an iPhone 3G from eBay in which the seller says the phone has been unlocked, successfully used with T-Mobile, and upgraded to OS 3.1.2. I put my T-Mobile SIM card in but the phone locked and I am not able to slide to unlock or slide to power off. I have soft reset it a couple of times but nothing has worked.

Just to clarify, the slide to unlock/power off bars slide but they do not slide all the way and stop and the same point. I was able to slide to unlock the phone before putting my SIM card in, but now sliding the bars will not work with or without the SIM card. I have already synced the iPhone on iTunes and that hasn't changed anything either.

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.